In a medium bowl, whisk together the lime juice, fish sauce, sesame oil, tamari, garlic, and red pepper flakes.
Slice the cucumbers into ¼ inch thick slices using a sharp knife or a mandolin slicer. Transfer to a bowl and add the green onion.
Add dressing just before serving and toss to combine. Sprinkle with the chopped cilantro and sesame seeds.
